Superconducting Transition Temperatures and Transport Properties of LaFe1-yRuyAsO0.89F0.11and LaFeAsO0.89-xF0.11+x

Satomi, Erika; Lee, Sang Chul; Kobayashi, Yoshihiko; Sato, Masatoshi

doi:10.1143/jpsj.79.094702

Cited by 30 publications

(40 citation statements)

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“…Comparison with the bulk case, x = 0.05 allows us to roughly estimate the SC volume fraction of the other samples, which becomes absolutely marginal above x = 0.5, confirming previous reports [8]. The shielding response is instead observable, but already much weaker for all samples with a reduced T c , at odds with the behavior of analogous Nd-1111 and La-1111 Ru-doped samples [10,11], suggesting that superconductivity is not a homogeneous bulk phenomenon in SmFe 1−x Ru x AsO 0.85 F 0.15 for x ≥ 0.1. We now turn to zero-field (ZF)-µSR results, sensitive to short range magnetic order, owing to the short range muon-spin coupling with the electronic moments.…”

supporting

confidence: 83%

Correlated Trends of Coexisting Magnetism and Superconductivity in Optimally Electron-Doped Oxypnictides

et al. 2011

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We report on the recovery of the short-range static magnetic order and on the concomitant degradation of the superconducting state in optimally F-doped SmFe1−xRuxAsO0.85F0.15 for 0.1 ≤ x 0.5. The two reduced order parameters coexist within nanometer-size domains in the FeAs layers and finally disappear around a common critical threshold xc ∼ 0.6. Superconductivity and magnetism are shown to be closely related to two distinct well-defined local electronic environments of the FeAs layers. The two transition temperatures, controlled by the isoelectronic and diamagnetic Ru substitution, scale with the volume fraction of the corresponding environments. This fact indicates that superconductivity is assisted by magnetic fluctuations, which are frozen whenever a short-range static order appears, and totally vanish above the magnetic dilution threshold xc.The appearance of high-T c superconductivity (SC) close to the disruption of static magnetic (M) order is a general feature of the Fe-based superconductors either as a function of doping or external pressure. In the REFeAsO family (RE1111) it is found that SC and M strongly compete and hardly coexist simultaneously [1, 2], apart for RE=Sm and Ce [3,4] within a small doping range where both order parameters are depressed. Coexistence implies short range magnetic order, that is detected only by local probes such as muon-spin rotation (µSR) [4] or nuclear quadrupole resonance (NQR) [5], since it eludes long coherence probes such as powder diffraction [6]. The competition between the superconducting and magnetic ground-states must be reconciled with the prevailing models of pairing mediated by spin fluctuations [7]. These models are seemingly in contradiction with the evidence that the two mutually excluding orders coexist only when phase separation occurs.Here we show, by means of µSR and 75 As NQR, that magnetism is surprisingly still at play in optimally F-doped SmFe 1−x Ru x AsO 0.85 F 0.15 . The isoelectronic Fe:Ru substitution is found to deteriorate the superconducting state in optimally electron-doped SmFeAsO 0.85 -F 0.15 samples and simultaneously to recover static magnetism within the FeAs layers, for 0.1 ≤ x 0.5. This is accompanied by a local electronic rearrangement within the FeAs layers. When Ru doping approaches the critical threshold x c = 0.6, corresponding to percolation of a magnetic square lattice with nearest neighbor (n.n.) and next-nearest neighbor hopping, both magnetism and SC vanish.The investigated polycrystalline SmFe 1−x Ru x AsO 0.85 -F 0.15 samples are the same of Ref. 8. From 19 F nuclear magnetic resonance the relative fluorine content was found to be constant within ∆ 0.01 in the whole set of samples investigated. To investigate the bulk character of the superconducting state we carried out transverse field (TF)-µSR measurements, where a sample is fieldcooled (FC) in a magnetic field larger than the lower superconducting critical field H c1 , applied perpendicular to the initial muon-spin orientation (H ⊥ S µ ). A flux-line lattice (FLL) i...

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confidence: 83%

Correlated Trends of Coexisting Magnetism and Superconductivity in Optimally Electron-Doped Oxypnictides

et al. 2011

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“…The behaviors of T c suppression by impurity doping in both RFeAs(O,F) and LaFeP(O,F) are very similar, i.e., the magnetic impurity of Mn strongly reduces T c , while the nonmagnetic impurities do not largely destabilize the SC state [29][30][31][32]. The previous and present experimental results may have indicated that these effects of destabilization of superconductivity by magnetic and nonmagnetic impurities are a common feature in iron-based SC materials.…”

Section: Discussionsupporting

confidence: 62%

Superconducting Gap Symmetry of LaFeP(O,F) Observed by Impurity Doping Effect

2016

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Abstract:We have investigated Mn, Co and Ni substitution effects on polycrystalline samples of LaFePO 0.95 F 0.05 by resistivity and magnetoresistance measurements. In LaFe 1-x M x PO 0.95 F 0.05 (M = Mn, Co and Ni), the superconducting transition temperature (T c ) monotonously decreases with increasing the impurity doping level of x. There is a clear difference of T c suppression rates among Mn, Co and Ni doping cases, and the decreasing rate of T c by Mn doping as a magnetic impurity is larger than those by the nonmagnetic doping impurities (Co/Ni). This result indicates that in LaFePO 0.95 F 0.05 , T c is rapidly suppressed by the pair-breaking effect of magnetic impurities, and the pairing symmetry is a full-gapped s-wave. In the nonmagnetic impurity-doped systems, the residual resistivity in the normal state has nearly the same value when T c becomes zero. The residual resistivity value is almost consistent with the universal value of sheet resistance for two-dimensional superconductors, suggesting that T c is suppressed by electron localization in Co/Ni-doped LaFePO 0.95 F 0.05 .

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“…Measurements of the microscopic quantities have also been carried out by means of NMR and neutron scattering. 15) First, we show very briefly important results of the previous studies, [4][5][6][7][8][9][10][11][12][13][14][15] which indicate that the S ++ symmetry is quite likely. Then, the magnetic excitation spectra "(q, ) obtained for a sample of Ba(Fe 0.9 Co 0.1 ) 2 As 2 , consisting of about three hundred pieces of crystallites are shown, and used in the arguments whether the data support the symmetry extracted above.…”

Section: Introductionmentioning

confidence: 64%

“…First, effects of impurity-doping on the superconducting transition temperature T c of the systems have been mainly studied by several members of our group [4][5][6][7][8][9][10][11][12][13][14][15] for the following reasons. The spin-fluctuation mechanism predicts the S symmetry, 2,3) where the signs of the superconducting order parameters are opposite between the disconnected Fermi surfaces around the and M points in the reciprocal space.…”

Section: Introductionmentioning

confidence: 99%

“…In the studies, [4][5][6][7][8][9][10][11][12][13][14][15] samples of LnFe 1 y M y AsO 0.89 F 0.11 (Ln= La, Nd; M=Co, Ni, Ru, Mn) and LaFeAsO 1 x F x have been used to examine macroscopic quantities, such as the electrical resistivities , Hall coefficients R H , thermoelectric powers S, magnetic susceptibilities and specific heats C). Measurements of the microscopic quantities have also been carried out by means of NMR and neutron scattering.…”

Section: Introductionmentioning

confidence: 99%

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On the Magnetic Excitation Spectra of Ba(Fe_0.9Co_0.1)₂As₂in the Superconducting State

et al. 2011

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Magnetic excitation spectra of Ba(Fe 0.9 Co 0.1 ) 2 As 2 obtained for aligned crystals with the superconducting transition temperature T c 23 K are presented after an overview of results of our preceding studies on the symmetry of the order parameter . Although many researchers have reported that their experimental results are consistently explained by the so-called S symmetry, and believe that the spin-fluctuation is relevant to the superconducting mechanism of Fe pnictide superconductors. However, the situation is not so simple, because almost all these data can be understood by the S ++ -symmetry, too. Furthermore, as we first pointed out and discussed in detail, the rates of the T c suppression by nonmagnetic impurities can hardly be explained by the S symmetry. Here, we show our own data of the magnetic excitation spectra of Ba(Fe 0.9 Co 0.1 ) 2 As 2 , and discuss which one of the S and S ++ -symmetries can better describe the characteristics of the peak observed there. These processes are important, because the S and S ++ symmetries are connected with the spin-fluctuation mechanism and a newly proposed one related to the orbital degrees of freedom of the systems, respectively.

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Superconducting Transition Temperatures and Transport Properties of LaFe_1-yRu_yAsO_0.89F_0.11and LaFeAsO_0.89-xF_0.11+x

Cited by 30 publications

References 24 publications

Correlated Trends of Coexisting Magnetism and Superconductivity in Optimally Electron-Doped Oxypnictides

Correlated Trends of Coexisting Magnetism and Superconductivity in Optimally Electron-Doped Oxypnictides

Superconducting Gap Symmetry of LaFeP(O,F) Observed by Impurity Doping Effect

On the Magnetic Excitation Spectra of Ba(Fe_0.9Co_0.1)₂As₂in the Superconducting State

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Superconducting Transition Temperatures and Transport Properties of LaFe1-yRuyAsO0.89F0.11and LaFeAsO0.89-xF0.11+x

Cited by 30 publications

References 24 publications

Correlated Trends of Coexisting Magnetism and Superconductivity in Optimally Electron-Doped Oxypnictides

Correlated Trends of Coexisting Magnetism and Superconductivity in Optimally Electron-Doped Oxypnictides

Superconducting Gap Symmetry of LaFeP(O,F) Observed by Impurity Doping Effect

On the Magnetic Excitation Spectra of Ba(Fe0.9Co0.1)2As2in the Superconducting State

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Superconducting Transition Temperatures and Transport Properties of LaFe_1-yRu_yAsO_0.89F_0.11and LaFeAsO_0.89-xF_0.11+x

On the Magnetic Excitation Spectra of Ba(Fe_0.9Co_0.1)₂As₂in the Superconducting State